Origin of the energy barrier that opposes proton surface-to-bulk release

Description

The concept of surface coupled proton exchange between membrane proteins has long been criticized because the origin of proton’s surface affinity remained enigmatic. The weak dependence of both migration speed and span on lipid composition suggests that interfacial water serves as proton railways (1). However, it is unclear how to reconcile the apparent high proton affinity to the phase boundary (2) with the poor proton acceptability of water. Here we monitored the diffusion of excess protons along the phosphatidylcholine lipid bilayer/water interface at different temperatures. The kinetics of proton arrival from a distant spot of proton release to lipid anchored fluorescent pH-sensitive dyes indicated that the in vitro Gibbs activation energy ΔG for proton surfaceto- bulk release harbours only a minor enthalpic constituent. Our observation that more than 2/3 of ΔG are entropic in origin explains the high proton affinity to membranes in the absence of a potent proton acceptor. This work was supported by Grant P25981 from the Austrian Science Fund (FWF) to P.P. 1. Springer et al. (2011) 108, 14466. 2. Zhang et al. (2012) 109, 9744. E. Weichselbaum, D. Knyazev, P. Pohl

Period	21 Jul 2015
Event title	European Biophysical Societies'
Event type	Conference
Location	GermanyShow on map